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Introduction to Aneuploidy
Introduction
Aneuploidy is a chromosomal anomaly in which the number of one or more chromosomes is abnormal. Normal human somatic cells (i.e., nonegg or sperm cells) carry 46 chromosomes: two copies of each of the 22 autosomal chromosomes and two sex chromosomes, either XX for female or XY for male. Monosomy and trisomy conditions result from the subtraction or addition of chromosomal material, respectively.
Aneuploid conditions are often suspected by prenatal ultrasound (US) when multiple, and sometimes severe, structural anomalies are seen. Different aneuploid conditions are typically associated with specific constellations of US findings. US on its own, however, is an insufficient screening tool for aneuploidy. Other methods, including serum biomarkers and noninvasive prenatal screening, should also be a part of a comprehensive prenatal screening program.
Disorder
Definition
Aneuploidy refers to an abnormal copy number of one or more chromosomes. Aneuploid conditions have a subtraction (monosomy) or an addition (trisomy) of chromosomal material in one or more of the chromosome pairs.
Polyploidy refers to an abnormal copy number of all of the chromosomes. The normal human cell is diploid, meaning it contains two copies of genetic material, with one copy coming from each parent. A triploid cell has 69 chromosomes (69, XXX, 69 XXY, 69, XYY) and thus three copies of genetic material. Triploidy is most commonly the result of ovum fertilization by two spermatozoa. It is not compatible with life and usually ends in pregnancy loss in the first trimester. The rare fetuses born alive usually die shortly after birth.
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